Field of the Invention
The present disclosure relates to inks, ink containers, image forming methods, image forming apparatuses, and image formed matters.
Description of the Related Art
In recent years, image forming methods have been spreading rapidly, for the reasons that image forming methods enable easy recording of color images and running costs of image forming methods are low.
Water-based pigment inks obtained by dispersing a pigment in water in a state of particles are paid attention as inks to be used in the image forming methods. Pigments have close compositions to colorants used in common commercial printing inks and are hence expected to be able to provide printed matters with close tones to commercially printed matters. However, when the water-based pigment inks are recorded over coat paper for commercial printing or publication printing, there occurs a lag in ink absorption, leading to a problem of beading.
Hence, the present applicant has previously proposed inkjet recording inks containing water, a water-soluble organic solvent, a surfactant, and a colorant (see, e.g., Japanese Unexamined Patent Application Publication Nos. 2012-207202 and 2014-94998). A polyvalent alcohol, a predetermined amide compound, etc. that have an equilibrium water content of greater than or equal to 30% at a temperature of 23° C. and a relative humidity of 80% are used as the water-soluble organic solvent. At least one selected from the group consisting of silicone-based surfactants, fluorosurfactants, and acetyleneglycol-based surfactants is used as the surfactant.
However, these proposals have not achieved optimization in a relationship between a dynamic surface tension of the inks at a surface lifetime, measured by a maximum foaming pressure method, of 15 msec and a static surface tension of the inks. Therefore, there is a problem that the inks are wettable over an ink-repellent film over a nozzle plate of an ink head and adhere to the nozzles to degrade discharging stability.